Neurons in the human visual cortex were demonstrated to possess an intensely negatively charged surface coat which was stained with çationic iron colloid and aldehyde fuchsin. Digestion with hyaluronidase eliminated both the iron colloid and fuchsin stainings of the coats. Treatment with chondroitinase ABC, heparitinase and kera-tanase eliminated the iron colloid staining of the coats, but did not interfere with the fuchsin staining. Electron microscopy of ultrathin sections revealed that the cationic iron particles were preferentially deposited in the perineuronal tissue spaces. These findings indicate that the surface coats consist of sulfated proteoglycans, which, as an extracellular matrix, occupy the perineuronal tissue spaces. This study further demonstrates that neurons with such surface coats are identical with neurons labeled with lectin Vicia villosa agglutinin. The cell surface glycoproteins reactive to this lectin may not be the structural elements of the sulfated coats since the lectin labeling was not interrupted by the hyaluronidase digestion.
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